Purification of crude cellulosic material



Patented Sept. 17, 1946 PURIFICATION OF CRUDE CELLULOSIC MATERIAL GeorgeP, Vincent, Poughkeepsie, N. Y.-, and ArchieL. Dubeau, Rumfcrd, R. I.,assignors to The Mathieson Alkaii VJorks, Inc., New York, N. Y, acorporation of Virginia,

No Drawing. Application September 18, 1940-, Serial No. 357,281

4 Claims. 1

This invention relates to the purification of crude cellulosic vegetablematerial, such as ground wood, cotton linters and carding waste, whichcontain large proportions of natural noncellulosic impurities such, forexample, as lignin. The invention contemplates the production from suchmaterials of relatively pure cellulose suitable for acetylation,nitration and other uses, including paper manufacture. In one of itsaspects, the invention contemplates improvements for controlling theviscositycharacteristic of the. celluloss product.- l I In accordancewith our invention, the crude cellulosic vegetable material to bepurified, for example ground wood, cotton linters, carding Waste,bagasse and the like, is subjected to a twostage steaming whileimpregnated'with hot aque-' ous liquors. In the first of said stages thematerial is exposed to the action of steam while impregnated with adecidedly alkaline aqueous solution ofcaustic soda, that is, onecontaining at least about 4% of caustic soda. in the second steamingoperation the material, arteran intermediate water washing, is exposedto the action of steam while impregnated with an acid aque-. oussolution sediuin chlo'rite, in amount effective to eliminate asubstantial part of the non-cellulose impurities remaining in thematerial; These steaming operations are carried out in a steam chamberand are of considerable duration, gen-* erally of the order of ahalf-hour or more. With cotton linters, carding waste and similarlowgrade cotton plant Icy-products, the preferred preliminary treatmentinvolves exposure in the presence of steam'to the action of a hotalkaline aqueous solution containing a detergent.

Control of the viscosity characteristic of-the cellulose product may beaccomplishedadvantageously by treating the cellulosic material,prefera-bly at an intermediate stage, with an aqueous hypochloritesolution pre'ferably in a cold state. Thus, sodium hypochloritesolutions tend to reduce the viscosity characteristic of the celluloseand also aid in impurity removal. When control of the viscositycharacteristic important, as when the purified cellulose is to beconverted into nitrate, acetate or other esters, hypochlorite treatmentis especially recommended, for by regulating the contact of the materialwith the hypochldrite through control of the time of treatment or theconcentration of the hypochlorite, Viscosity characteristics maybealtered at will.

To consider in somewhat greater detail the purification of linters andsimilar low-grade byproducts of cotton ginning, carding and similarcotton-cleaning processes, our preferred preliminary treatment involvesstearning the material while it is impregnated with a decidedly'alkalinesolution, containing at least 4% caustic soda, and also containing asuitable detergent, i. e., one that is active in alkaline solution. Awide variety of detergents may be employedsince common soaps andnumerous synthetic detergents are activ in alkaline solution. Ifhypochlo'rite treatment is employed, this should follow thealkali-steaming stage. In any case, thelater treatment involves theexposure of the material, in the presence. of steam, to the action of ahot acid solution containing sodium chlorite and, preferably, alsocontaining a detergent that is active in acid-solution,

, such,.for example, as sodium ocenol sulfates, boro iii) cetyl alcoholand sodium alkyl sulionate benzene.

Certain synthetic organic detergents, for example, .Modinalfl which is acompletely sulfated sodium ocenol sulfate, are active in acid and a1-kaline solutions and may be employed in the preliminary alkaline stageand in the acid-chlorite stage.

Alkalinity may be imparted to the preliminary treatment liquors withvarious reagents, but so dium hydroxide is preferred.

. A- Variety of acids may be employed to acidify Example A.-Two-stage'treatment for raw cotton linters A quantity of linters is immersed in asolution containing 12% sodium hydroxide, and .5% of a detergent, say,Modinal/i After immersion, the linters are squeezed to drive out excesssolution and leave a ratioot two parts by Weight of solution to one partby Weight of solid. The resulting Wet linters is then introduced into asteam chamber and held at 100 C. for about onehalf hour in the presenceof the steam. "Thereafter, the partially purified linters is Washed withhot water.

- The washed linters is immersed in a solution containing 1% availablechlorine (C12) as sodium chlorite, 5% of a suitable detergent, sayModinal, and 3% by weight of acetic acid (56% strength). The linters isthen squeezed to remove excess solution and leave a ratio of two partsby Weight of solution to one part by weight of solid. The wet linters isthen held at a tem- Example B.-Three-staqe treatment of raw cot-- tonlinters In this instance, a mass of dry raw linters was immersed in asolution containing 8% sodium hydroxide and .5% Modinal. It was thensqueezed to leave two parts by weight of solution to one part by weightof solid and the resulting wet pulp was held for one-half hour at 100 C.in a steam chamber. It was then washed in hot water.

The washed mass was immersed in a 1% by weight aqueous solution ofsodium hvpochlorite and then squeezed to leave a 2:1 liquor to solidratio therein. The squeezed mass was left at room temperature(approximately 30 C.) for about half an hour and then washed in coldwater.

The washed mass from the second-stage was immersed in the solutioncontaining .5% available chlorine as sodium chlorite, .5% Modinal and 1%acetic acid (56%). After immersion, the mass/Was squeezed to removeexcess liquor and leave a ratio of 2:1 liquor to solids. Thereafter, themass was held at 100 C. for about half an hour in a steam chamber andfinally washed with hot water.

The resulting product was satisfactory for use in acetylation, nitrationand the like, and was fully as white asv standard purified lintersemployed heretofore in such processes.

Very low-grade linters (cotton seed hull fiber) containing an especiallyhigh proportion of impurities may also be treated advantageously inaccordance with the process of our invention in two or three stages.

Example. C,--Two-stage treatment of low-grade linters A mass of drylinters (cotton seed hull fiber) was immersed in an aqueous solutioncontaining 12% sodium hydroxide and .5% Modinal and squeezed to removeexcess liquor and leave a 2:1 liquor. to solid ratio. The mass was thenheld at 100 C. for about half an hour in a stem chamber and thereafterwashed in hot water.

The washed mass was immersed in an aqueous liquor containing 1%available chlorine as sodium chlorite, .5% Modinal and 3% acetic acid(56%). After immersion,'the mass was squeezed to remove excess liquorand leave a 2:1 liquor to solid ratio. The mass was then steamed in achamber for one-half an hour at 100 C. and finally washed with hotwater.

The resulting cellulose was suitable for acetylation and comparedfavorably in whiteness with that produced according to Examples A and Bfrom ordinary raw linters.

Example D.Three-stage treatment of loin-grade raw linters mersed in asodium hypochlorite solution containing 1% available chlorine and, as inthe previous cases, thereafter squeezed to leave a ratio of 2:1 liquorto solids. The squeezed mass was then held at room temperature for halfan hour and thereafter washed with hot water. 1

In the third stage, the mass from the previous treatments was immersedin a solution containing .5% available chlorine as sodium chlorite, .5%Modinal and 1% acetic acid (56%). After immersion, the mass was squeezedto leave two parts by weight of liquor to one part by weight of solidsand the mass was then held at 100 C. for about one-halfhour in the steamchamber. hot water.

The resulting cellulose had a whiteness of and was at least as good asthat heretofore customarily employed in acetylation.

Linters which have been cooked in the usual way and so partiallycleansed may also. be treated with advantage in accordance With ourinvention. Such treatment, however, need not employ such strongsolutions as those employed in the treatment of raw and low-gradelinters. Treatment of cooked linters in accordance with ourinvention isillustrated by the following example:

Example E.--Two-stage treatment of cooked linters The washed linters wasimmersed in a solution containing 25% available chlorine assodiumchlorite, .5% Modinal and .5%" acetic acid (56%). After immersion,the mass was squeezed to leave two partsby weight of liquor' to one partby weight of solids and thereafter held for about one-half hour at C. ina steam chamber. After heating, the material was washed with hot water.

As in the previous cases, the resulting product was comparablewith'cotton linters heretofore employed for acetylation purposes and wasof standard whiteness.

' In the treatment of low-grade cotton byproducts, such as cardingwaste, the process of the invention also offers advantages. Applica- Ytion of the process to carding waste with a very high percentage ofimpurities and which contained whole seeds is illustrated by thefollowing example:

Example F.T'wo-stage treatment of carding waste The dry carding waste(card strip waste) was immersed in a solution containing 8% sodiumhydroxide and .5% Modinal, squeezed to leave a 2:1 liquor to solid ratioand held at 100 C. for about one-half an hour in a steam chamber. It wasthen washed with hot water.

The washed material was immersed in a solution containing 1%availablechlorine as sodium chlorite, .5% Modinal and 2% acetic acid(56%). After immersion, material was squeezed to leave a 2:1 liquor tosolid ratio, held at 100 C. for about one-half hour in a steam chamberand thereafter washed with hot water.

Finally, the mass was washed with The resulting material was bleached toa color as good as that obtained in the foregoing examples and ingeneral all non-:cellulosic impurities were removed. The productcontained a few partially bleached hulls.

We claim:

1. A process for purifying crude cellulosic vegetable materials whichcomprises impregnating said material with an alkaline aqueous solutioncontaining about 4 to 12% of caustic soda, discharging solution from thematerial until the ratio by weight of solution remaining in the mat rialto the material is about 2:1, exposing the said material while wet withthe solution to the action of steam for a period of at least aboutone-half hour in a steam chamber, thereafter washing the material withwater, impregnating it with an acid aqueous solution containing sodiumchlorite in amount efiective to eliminate a substantial part of thenon-cellulose impurities remaining in the material, discharging solutiontherefrom until the ratio by weight of solution remaining in thematerial to the material is about 2:1, and exposing the said materialwhile wet with the second said solution to'the action of steam for aperiod of at least about one-half hour in a steam chamber.

2. A rocess for purifying crude cellulosic vegetable materials whichcomprises impregnating said material with an alkaline aqueous solutioncontaining about 4 to 12% of caustic soda and a detergent, dischargingsolution from the material until the ratio by weight of solutionremaining in the material to the material is about 2:1,

exposing the said material while wet with the I solution to the actionof steam for a period of at least about one-half hour in a steamchamber, thereafter washing the material with water, impregnating itwith an acid aqueous solution containing sodium chlorite in amounteffective to eliminate a substantial part of the non-celluloseimpurities remaining in the material, discharging solution therefromuntil the ratio by weight of solution remaining in the material to thematerial is about 2: 1, and exposing the said material while wet withthe second said solution to the action of steam for a period of at leastabout onehalf hour in a steam chamber.

3. A process for purifying crude cellulosic vegetable materials whichcomprises impregnating said material with an alkaline aqueous solutioncontaining about 4 to 12% of caustic soda, discharging solution from thematerial until the ratio by weight of solution remaining in the materialto the material is about 2:1, exposing the said material while wet withthe solution to the action of steam for a period of at least aboutonehalf hour in a steam chamber, thereafter washing the material withwater, impregnating it with an acid aqueous solution containing adetergent and sodium chlorite, discharging solution. therefrom until theratio by weight of solution remaining in the material to the material isabout 2:1, and exposing the said material while wet with the second saidsolution to the action of steam for a period of at least about one-halfhour in a steam chamber.

4. A process for purifying crude cellulosic vegetable materials whichcomprises impregnating said material with an alkaline aqueous solutioncontaining about 4 to 12% of caustic soda, discharging solution from thematerial until the ratio by weight of solution remaining in the materialto the material is about 2:1, exposing the material while wet withthe'solution to the action of steam for a period of at least aboutonehalf hour in a steam chamber, thereafter washing the material withwater, subjecting the washed cellulosic material to the action of anaqueous solution containing sodium hypochlorite in amount effective toeliminate a substantial part of the non-cellulose impurities remainingin the material, regulating the contact of the cellulosic material withthe hypochlorite solution to control the viscosity characteristic of thefinal cellulosic product, thereafter washing the material with water,impregnating it with an acid aqueous solution of sodium chlorite,discharging solution therefrom until the ratio by weight of solutionremaining in the material to the material is about 221, and exposing thesaid material while wet with the last said solution to the action ofsteam for a period of at least about onehalf hour in a steam chamber.

GEORGE P. VINCENT. ARCHIE L. DUBEAU.

